Selected Acronyms
CM Cable Modem
CPE Customer Premises Equipment (connects to CM)
CMTS Cable Modem Termination System (maybe integrated or modular)
DOCSIS Data Over Cable Service Interface Specification
DSBG Downstream Bonding Group
DSID Downstream Service Identifier
CMCI-Port Physical interface to which CPE can attach to a CM
IGMP Internet Group Management Protocol (IPv4)
PCMM Packet Cable Multimedia
Data Over Cable Service Introduction
Cable operators have widely deployed high-speed data services on cable television systems. These data services allow subscriber-side devices, such as personal computers, to communicate over an ordinary cable TV network Hybrid Fiber Coax (HFC) cable. Cable Television Laboratories, Inc. (CableLabs®) publishes detailed technical specifications for such systems, including DOCSIS—Data Over Cable Service Interface Specification. Referring to FIG. 1, in a cable system 100, a Cable Modem Termination System (CMTS) 102 (or a modular CMTS called “M-CMTS”) connects the cable network 104 to a data network, such as the Internet 106. In a modular CMTS architecture the DS MAC and PHY are separated, with the MAC residing in the M-CMTS core and the DS PHY being a part of the external EQAMs. (Some systems may utilize a Universal Edge QAM device, or “UEQAM” for short, which typically comprises a chassis having one or more gigabit Ethernet (GigE) input ports, and multiple QAM modulators and RF upconverters on the output (downstream) side.) A downstream QAM 110 receives data transferred from the CMTS over a packet switched portion of the network, performs modulation and other processing, and then transfers the modulated data over a Hybrid Fiber Coaxial (HFC) portion 120 of the cable network to subscribers. This is called the “downstream” direction.
In general, this HFC or coax cable feeds the last link (for example, over the last half mile or less) to an individual home or other structure. There, a cable modem (CM) 130 may provide a packet interface, for example Ethernet compliant, to various consumer premises equipment (CPE) 132 such as a personal computer. The CM may be connected to a hub or router (not shown), for example to implement a home network, wireless access, etc. The CM (or a second CM) may be implemented in other equipment, for example a “set-top-box” (STB) 140 which provides an interface to a television or other video display 142. A CM may serve multiple subscriber devices or “clients” on separate interfaces.
DOCSIS specifies that the cable modems obtain upstream bandwidth according to a request/grant scheme because the upstream channel is shared. A cable modem sends a bandwidth allocation request when it receives a packet from a subscriber device and the packet needs to be sent upstream into the cable network. The CMTS scheduler grants these requests using bandwidth allocation map (“MAP”) messages. MAP messages inform the CMs about specific allocations of upstream spectrum in the time dimension, using time slots or “minislots.” The requesting modem then waits for its scheduled time before it can begin transmission. In this way, the system avoids collisions in upstream transmissions from multiple CMs.
In addition, individual CMs are assigned to specific frequency “channels.” In this way, more than one CM may actually transmit at the same time, but they are separated by frequency division multiplexing. DOCSIS 3.0 allows a single CM to transmit on multiple upstreams (channels), as further discussed below. In other words, a DOCSIS 3.0 enabled CM may have multiple transceivers simultaneously operable at different frequencies. In some newer wideband CMs, a single transceiver may be tunable over multiple channels, within a given frequency range. DOCSIS 3.0 CM operate on at least four frequency channels concurrently.
Recently, especially in newer communities, service providers (or developers) are implementing fiber to the home (FTTH), in other words, running “fiber” or “glass” (optical fiber cable) all the way from the head and or distribution hub to the home. FTTH is desirable because it can carry high-speed broadband services integrating voice, data and video. Accordingly, separate traditional telephone lines (copper) may no longer be necessary. And coax to the home for internet access and television programming may be obviated as well. RF over Fiber (“RFoG”) is advantageous because the analog RF signals transmitted over fiber (in the form of photons) incur little loss, even over run lengths of many miles, whereas losses over coax can be significant, requiring the use of repeaters or amplifier equipment every 1000 to 2000 feet. Fiber is also essentially immune to EM interference and unauthorized eavesdropping. In many existing systems, fiber runs only to a “Fibernode,” from which point coax is used for the remaining segment to individual homes or office.
Television and Other Streaming Video
Cable networks such as those described above have been widely deployed. Many households and businesses rely on cable modem connectivity for email and other Internet access. And many customers enjoy television programming delivery via the cable networks. “Cable TV” today comprises forwarding of both analog and digital broadcast television, as well as cable stations, i.e. stations that broadcast only via the cable network (as well as radio programming and some other services). The use of digital protocols such as IP (Internet Protocol) for streaming video content offers significant benefits. Among them is the ability to provide “IPTV” service in which a customer can select among a menu of digital TV stations or other digital content as explained below.
Several preferred examples of the present invention will now be described with reference to the accompanying drawings. Various other examples of the invention are also possible and practical. This application may be exemplified in many different forms and should not be construed as being limited to the examples set forth herein.